In general, sprinkler systems, particularly those used in inground systems, include a sprinkler head which contains a sprinkler nozzle and mechanisms for controlling the fluid flow through the head to the nozzle. Rotating sprinkler nozzles include a mechanism for rotating the nozzle as a function of input fluid flow rates using the fluid flow through the head to rotate a drive mechanism to rotate the nozzle.
The drive mechanism for such rotatable sprinklers generally include an impeller actuated by fluid flow and a transmission which converts rotation of the impeller to rotation of the nozzle. Various types of nozzles can be used on such sprinklers to provide various types of spray patterns. An example of a pattern sprinkler head is taught in U.S. Pat. No. 4,471,908 to Hunter, also assigned to the assignee of the present invention.
With such sprinkler systems, a wide variation in fluid flow out of the nozzle can be obtained. However, for providing a consistent, predictable watering pattern and volume and to prevent excessive wear on the rotating parts of the system, it is desirable to control the rate of rotation of the nozzle and preferably to keep the rate relatively constant. Various mechanisms have been used for controlling the fluid flow rate to the impeller to control the rate of rotation of the nozzle.
One device for controlling the rate of rotation is the stator mechanism which has been previously used by The Toro Company, the assignee of the present invention, in certain sprinkler heads. That stator mechanism comprises a spring loaded valve which can move toward and away from a valve seat under the influence of water pressure and which is located immediately beneath the impeller. That area of the stator surrounding the valve seat is provided with two drive ports which are constantly open. These drive ports are arranged to direct a relatively constant amount of water flow against the blades of the impeller regardless of the amount of incoming water pressure or volume of water. However, if such higher pressures or volumes of incoming water are present, the spring loaded valve opens and this "excess" water is directed up through a plurality of holes in the center of the impeller and is not directed against the turbine blades.
Although the stator mechanism described above is acceptable, it is a mechanically complicated device requiring a valve head, valve seat and spring to be assembled together. In addition, because of its complexity and design it creates undesirable turbulence within the sprinkler head which can cause undesirable wear on the impeller and other parts of the head. For example, the location of the valve head and spring directly in the path of incoming fluid creates turbulence as does the passing of the "excess water" from the valve head through the holes in the center of the impeller. Turbulence can decrease the effectiveness of the stator in controlling fluid flow rates. For this reason, it would be advantageous to have a stator design for controlling the rate of fluid flow through the head which minimizes turbulence and requires a minimum of mechanical parts.